Nitride semiconductor device and fabrication method therefor

Abstract

A nitride semiconductor device includes an electron transit layer ( 103 ) that is formed of a nitride semiconductor, an electron supply layer ( 104 ) that is formed on the electron transit layer ( 103 ), that is formed of a nitride semiconductor whose composition is different from the electron transit layer ( 103 ) and that has a recess ( 109 ) which reaches the electron transit layer ( 103 ) from a surface, a thermal oxide film ( 111 ) that is formed on the surface of the electron transit layer ( 103 ) exposed within the recess ( 109 ), a gate insulating film ( 110 ) that is embedded within the recess ( 109 ) so as to be in contact with the thermal oxide film ( 111 ), a gate electrode ( 108 ) that is formed on the gate insulating film ( 110 ) and that is opposite to the electron transit layer ( 103 ) across the thermal oxide film ( 111 ) and the gate insulating film ( 110 ), and a source electrode ( 106 ) and a drain electrode ( 107 ) that are provided on the electron supply layer ( 104 ) at an interval such that the gate electrode ( 108 ) intervenes therebetween.

What is claimed is: 
     
       1. A nitride semiconductor device comprising:
 a substrate; 
 an electron transit layer that is formed on the substrate, and that is formed of a nitride semiconductor; 
 an electron supply layer that is formed on the electron transit layer, and that is formed of a nitride semiconductor whose composition is different from the electron transit layer; 
 a passivation film formed on the electron transit layer, the passivation film including a first layer and a second layer stacked on the first layer; 
 a first electrode that penetrates through the first layer, and is covered with the second layer; 
 a second electrode that penetrates through the first layer, and is covered with the second layer; 
 a gate electrode that opposes the electron transit layer between the first electrode and the second electrode, the gate electrode arranged at a position closer to the first electrode than to the second electrode; and 
 a gate insulating film disposed between the gate electrode and the electron supply layer, the gate insulating film extending over the passivation film so as to cover the passivation film. 
 
     
     
       2. The nitride semiconductor device according to  claim 1 , wherein
 the first electrode is a source electrode, and 
 the second electrode is a drain electrode. 
 
     
     
       3. The nitride semiconductor device according to  claim 1 , further comprising an interlayer insulating film disposed on the gate insulating film. 
     
     
       4. The nitride semiconductor device according to  claim 3 , further comprising
 a source wiring film that is disposed on the interlayer insulating film and is electrically connected to the first electrode, and 
 a drain wiring film that is disposed on the interlayer insulating film and is electrically connected to the second electrode, 
 wherein the source wiring film and the drain wiring film are formed in a pattern that the source wiring film and the drain wiring film mesh with each other in a comb tooth shape. 
 
     
     
       5. The nitride semiconductor device according to  claim 1 , wherein the gate insulating film has a thickness ranging from 5 nm to 50 nm. 
     
     
       6. The nitride semiconductor device according to  claim 1 , wherein the gate insulating film is formed of Al 2 O 3 . 
     
     
       7. The nitride semiconductor device according to  claim 1 , wherein a combination of the electron supply layer/electron transit layer is any one of AlGaN layer/GaN layer, AlGaN layer/AlGaN layer (where Al composition is different), AlInN layer/AlGaN layer, AlInN layer/GaN layer, AlN layer/GaN layer and AlN layer/AlGaN layer. 
     
     
       8. The nitride semiconductor device according to  claim 1 , further comprising a cap layer that is formed on the electron supply layer, and that is formed of a nitride semiconductor having a same composition as the electron transit layer. 
     
     
       9. The nitride semiconductor device according to  claim 8 , wherein the cap layer has a thickness of 16 nm or less. 
     
     
       10. The nitride semiconductor device according to  claim 1 ,
 wherein the electron transit layer is a GaN layer having a thickness of 400 nm or more. 
 
     
     
       11. The nitride semiconductor device according to  claim 1 , further comprising an AlGaN buffer layer that intervenes between the substrate and the electron transit layer, and that includes a high aluminum composition region whose aluminum composition is relatively high and a low aluminum composition region whose aluminum composition is lower than the high aluminum composition region and which is arranged in a region close to the electron transit layer as compared with the high aluminum composition region. 
     
     
       12. The nitride semiconductor device according to  claim 11 , further comprising an element separation layer that passes through the electron supply layer and the electron transit layer to reach the AlGaN buffer layer. 
     
     
       13. The nitride semiconductor device according to  claim 12 , wherein the element separation layer is a high resistance layer that is formed by ion implantation from a direction inclined with respect to a direction of thickness of the electron transit layer, the ion implantation causing a crystal defect to increase a resistance of a region subject to the ion implantation. 
     
     
       14. The nitride semiconductor device according to  claim 11 ,
 wherein the AlGaN buffer layer is an AlGaN layer whose aluminum composition is adjusted such that as the AlGaN buffer layer approaches the electron transit layer in a direction of a layer thickness from the substrate toward the electron transit layer, the aluminum composition is decreased. 
 
     
     
       15. The nitride semiconductor device according to  claim 11 ,
 wherein the AlGaN buffer layer includes a first aluminum composition AlGaN layer that has a first aluminum composition and a second aluminum composition AlGaN layer that is deposited on a side of the electron transit layer with respect to the first aluminum composition AlGaN layer and that has a second aluminum composition lower than the first aluminum composition, and 
 the high aluminum composition region includes the first aluminum composition AlGaN layer, and the low aluminum composition region includes the second aluminum composition AlGaN layer. 
 
     
     
       16. The nitride semiconductor device according to  claim 11 , further comprising:
 an AlN buffer layer that intervenes between the AlGaN buffer layer and the substrate. 
 
     
     
       17. The nitride semiconductor device according to  claim 12 ,
 wherein the element separation layer is formed so as to surround an element region. 
 
     
     
       18. The nitride semiconductor device according to  claim 12 , further comprising:
 a wiring that is arranged on the element separation layer. 
 
     
     
       19. The nitride semiconductor device according to  claim 12 ,
 wherein the element separation layer is formed so as to separate a plurality of element regions, and 
 the nitride semiconductor device further comprises an element-to-element wiring that connects between a plurality of elements respectively formed in the element regions. 
 
     
     
       20. The nitride semiconductor device according to  claim 19 ,
 wherein the elements respectively formed in the element regions include two or more elements having different functions. 
 
     
     
       21. The nitride semiconductor device according to  claim 19 ,
 wherein the elements respectively formed in the element regions include two or more elements having a common function. 
 
     
     
       22. The nitride semiconductor device according to  claim 19 ,
 wherein the element separation layer is formed so as to surround the element regions of the elements connected with the element-to-element wiring. 
 
     
     
       23. The nitride semiconductor device according to  claim 12 ,
 wherein the element separation layer is a high resistance layer that is formed by ion implantation using, as a material, an element whose mass number is less than 10 but more than 2. 
 
     
     
       24. The nitride semiconductor device according to  claim 12 ,
 wherein the element separation layer is a high resistance layer that is formed by implantation of a helium ion. 
 
     
     
       25. The nitride semiconductor device according to  claim 12 ,
 wherein the element separation layer is a high resistance layer that is formed by ion implantation using a plurality of acceleration energies. 
 
     
     
       26. The nitride semiconductor device according to  claim 13 ,
 wherein an inclination angle of the ion implantation direction with respect to the direction of the thickness of the electron transit layer is 5 to 10 degrees. 
 
     
     
       27. The nitride semiconductor device according to  claim 12 ,
 wherein the gate electrode is formed so as to surround the first electrode together with the element separation layer. 
 
     
     
       28. The nitride semiconductor device according to  claim 1 , further comprising:
 an interlayer insulating film that covers the first electrode, the second electrode and the gate electrode; 
 a source wiring film that is connected to the first electrode via a source contact hole passing through the interlayer insulating film and that is arranged on the interlayer insulating film; and 
 a drain wiring film that is connected to the second electrode via a drain contact hole passing through the interlayer insulating film and that is arranged on the interlayer insulating film, 
 wherein the source wiring film and the drain wiring film are formed in such a pattern that, on the interlayer insulating film, the source wiring film and the drain wiring film mesh with each other in a comb tooth shape. 
 
     
     
       29. The nitride semiconductor device according to  claim 18 ,
 wherein the wiring includes a gate wiring connected to the gate electrode. 
 
     
     
       30. The nitride semiconductor device according to  claim 1 , wherein the passivation film is formed of silicon nitride. 
     
     
       31. The nitride semiconductor device according to  claim 1 , wherein the first electrode and the second electrode are formed on the first layer of the passivation film so as to partly cover the first layer.